The invention relates to a device for supporting a body lumen. More particularly, the invention is related to a stent formed from stent preforms. Each stent preform has a core that is completely isolated from the lumen walls for supporting a body lumen.
The importance of stents in modem medical treatments cannot be over-emphasized. Stents have revolutionized the care of patients by allowing far less invasive and risky surgical procedures to be undertaken. In coronary care, for example, complications following angioplasty can result in acute damage to artery walls, which prior to the development of stent technology required immediate bypass surgery. Stents are now recognized as a viable means of avoiding such procedures, because implantation of such a mechanical device into the area of concern allows the artery walls to be reinforced with permanent artificial scaffolding. Additionally, stents are now recognized as an effective modality for reducing the frequency of restenosis, the recurrent narrowing of the lumen (cavity or channel within a body tube).
Balloon treatment of narrowed arteries can initially increase the diameter of the artery by compressing blockage. However, recoil may result in lumen of insufficient diameter. Such recoil can be hindered by using a stent to dictate the diameter that the lumen is to assume.
Stent delivery and deployment may be performed by balloon mounting the stent and using a catheter to access the area of concern. By inflating the balloon at the lumen defect site, the stent may be expanded to the optimal size to support the lumen. Multiple stents may be deployed as necessary to accommodate defects of larger size or multiple defect locations.
Through the use of stent delivery systems, successful implantations can result in remarkable increase in blood flow, and over time new tissue growth in the area of the implant allows the lumen to maintain a typical structure.
It should be no surprise, however, that as a foreign object introduced into the body, the stent implant may also produce undesirable results. Among the problems encountered with implantation are tearing or cracking of the artery lining. In addition, the stent may irritate the lumen, resulting in blood clot formation on the stent itself. Serious consequences may result, including the need for further invasive procedures and concomitant increased risks.
Thus, there is a need for improved stents which minimize damage to the lumen as a result of interaction of the stent with the lumen, thereby allowing the management of acute vessel dissection and occlusion, decreasing the rate of restenosis, and increasing the safety and efficacy of stent treatments. There is also a need to reduce the frequency of stent thrombosis, the formation of solid masses from blood constituents caused by the thrombogenic surface of prior art stents, by providing a stent preform that when formed as a stent is less likely to damage the lumen.
Stents designed for use in arteries are currently fabricated in metal wireform or tubular shapes that are laser cut. Wireforms may be twisted or coiled mechanically using manual or automatic coil winding machines, or otherwise braided or knitted with similarly useful technology. Individual or multiple stent preforms may be used to create the stent. Prior art stents include metal-polymer composites, in which a metal layer is sandwiched between two layers of a polymer. Alternatively, the faces of the metal layer are coated using thin film deposition techniques, such as Pulsed Laser Deposition, which allow polymer films of micron-level thickness to be applied. The metal layer may also be sandwiched between two layers of biologic material.
The in vivo expansion of the stent using a balloon or other expansion device can create mechanical trauma at the site of application. When using a balloon, for example, the surface of the stent impacts the wall of the artery with a force equivalent to the pressurization of the balloon, and the trauma to the vessel wall from this impact can lead to undesirable tissue proliferation in the long-term. In almost one-quarter of all stent implantations, restenosis through tissue ingrowth occurs. The polymer-overlayer stents with exposed core ends cause inflamation and thrombosis. Furthermore, during the pulsatile force inside the artery, the stent continuously rubs against the artery wall, creating trauma in the region of the implant and to soft tissues of the vessel wall.
In this regard, the present invention is directed to a stent preform that isolates the core of the stent from the body lumen to prevent undesirable additional trauma in the lumen.
The present invention relates to a stent preform for implantation in a body lumen. The stent preform includes an elongated metal core having first and second core ends, a contact surface, and a solid cross-section, and a hollow outer sheath made of a biocompatible polymer and having first and second sheath ends, caps disposed on the sheath ends, and an interior surface. The outer sheath surrounds and contacts the contact surface of the core to prevent the core from directly contacting the body lumen.
The stent preform may include an elongated core that is expandable, and the outer sleeve may be capable of deforming to compensate for dimensional changes in the cross-section of the expanded core. The cross-section of the core of the stent preform may be substantially cylindrical.
The biocompatible polymer of the outer sheath may be formed of a heat-shrinkable polymer material. The outer sheath also may be formed from a polymer tape.
Preferably, the stent preform may include an elongated core that is formed of a shape-memory alloy. The outer sheath may be made of a polymer film having a thickness between about 0.1 micron and about 5 millimeters. In a preferred embodiment, the sheath caps of the stent preform have a generally rounded contour to minimize stress concentration along the walls of the lumen. The stent preform may also include a cover of a biological or synthetic coating to minimize interference of the stent preform with normal blood function. The coating may be an anticoagulent selected from the group of heparin, hirudin, coumadin, tichlopidiene, and chlopidogrel. The coating may also be disposed in micropores in the outer sheath, allowing controlled release of constituents of the coating.
In another embodiment, the stent preform includes an elongated metal core having first and second core ends, a contact surface, and a solid cross-section, at least one intermediate sleeve disposed between the outer sheath and the core, and a hollow outer sheath made of a biocompatible polymer and having first and second sheath ends, caps disposed on the sheath ends, and an interior surface. The outer sheath surrounds the intermediate sleeve and contact surface of the core to prevent the sleeve and core from directly contacting the body lumen.
The at least one intermediate sleeve may be a lubricious lining, with the core and the lining forming a composite body that is configured and dimensioned to be slidably received by the outer sheath. In a preferred embodiment, the outer sheath and the lining may form a composite body that is configured and dimensioned to be slidably received by the core.
In another embodiment, a filamentary member for implantation in a body lumen includes a rigid inner filament with first and second filament ends, and an outer sheath with first and second sheath ends. Preferably, the outer sheath is made of a biocompatible polymer, and the outer sheath completely encapsulates the inner filament to prevent the core from directly contacting a wall of a body lumen. The inner filament may be made of a plurality of woven fibers. The inner filament may be made from carbon fiber, kevlar, or glass fiber.
The present invention also relates to a method of making a stent preform. The method includes the steps of: providing an elongated core; completely surrounding the core with a polymer jacket to create a composite; heat treating the composite to promote bonding of the core and jacket; and bending the composite to a desired shape.
Preferably, the elongated core is made of metal. The metal may be a shape-memory alloy, and the polymer jacket may be formed of a biocompatible polymer.
In a preferred embodiment, the elongated core is expandable, and the polymer jacket is capable of deforming to compensate for dimensional changes in the cross-section of the expanded core.
The method may also include the step of heat treating the elongated core prior to encapsulating the core with a polymer jacket.
In a preferred embodiment, the polymer jacket is formed of a tape of a biocompatible polymer.
In another embodiment, a method of making a stent preform includes the steps of: providing an elongated metal core; completely encapsulating the core with a polymer tape to create a composite; and bending the composite to a desired shape. The tape may be a vascular fabric.
In another embodiment, a method of making a stent preform comprising the steps of: providing an elongated core made of a shape-memory material; completely encapsulating the core with a biocompatible fabric to create a composite; and bending the composite to a desired shape. At least one intermediate sleeve may be disposed between the biocompatible fabric and the core.